Field of the Invention
The present invention relates to an image display apparatus.
Description of Related Art
A head-up display (HUD) for displaying driving information on a windshield of a vehicle by superimposing the driving information on a driver's field of view has been developed. The driving information is, for example, information on a speed and car navigation. In a conventional HUD, vehicle information is invisible to both a driver and a fellow passenger sitting in a passenger seat due to a narrow viewing angle.
Thus, a display apparatus that allows a driver and a fellow passenger to view driving information by placing a half-mirror between a display body and a display unit to change an angle of a display surface on which an image is displayed has been proposed (for example, refer to Japanese Utility Model No. 63-158428 (hereinafter, Patent Document 1)). In addition, the display body is a fluorescent display tube or a liquid crystal panel, and driving information is displayed thereon. Also, the display unit is a semi-transparent mirror provided at an inner surface of a windshield of a vehicle, and a display light projected from the display body is projected on the display unit. With the technology described in Patent Document 1, a driver may view driving information that is transmitted through the half-mirror and displayed on the display unit, and a fellow passenger may view the driving information reflected by the half-mirror.
In addition, a display apparatus that projects driving information from a projector to a holographic optical system by placing the holographic optical system on a windshield has been proposed (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2011-180177 (hereinafter, Patent Document 2)). With the display apparatus described in Patent Document 2, a driver and a fellow passenger may view driving information when a projected image of the driving information is diffracted at two angles by an interference pattern pre-recorded in two or more layers of the holographic optical system. With the technology described in Patent Document 2, a driver may view a first diffracted light due to a first layer of a holographic optical element, and a fellow passenger may view a second diffracted light due to a second layer of the holographic optical element.